Tab. 5:

Categories of in vitro test methods

Category	Exposure	Example of a standard method or guidance document
1	Liquid exposure to suspended molecules or suspended cells	In chemico skin sensitization: direct peptide reactivity assay (DPRA) (OECD, 2019)
2	Submerged liquid exposure with cells at the bottom of wells	In vitro skin sensitization: The ARE-Nrf2 luciferase KeratinoSens test method (OECD, 2018c)
3	A liquid, cream, or solid is directly applied to a biological test system such as a 3D construct	In vitro skin irritation: reconstructed human epidermis test method (OECD, 2021a)
4	Airborne exposure to a biological test system located on an air-liquid interface insert	Considerations for in vitro studies of airborne nano-objects and their aggregates and agglomerates (ISO, 2020d)
5	Exposure via multiple routes using an in vitro microphysiological system (e.g., eye-on-a-chip, gut-on-a-chip, and lung-on-a-chip devices)	Standard methods or guidance documents are not yet published to our knowledge.